Tone ordered discrete multitone interleaver

ABSTRACT

A tone ordered discrete multitone interleaver system and method, including a tone ordered interleaver and deinterleaver, are provided for efficiently communicating data despite noise affecting a Discrete Multitone modulation (DMT) system. The tone ordered discrete multitone interleaver forces interleaving of trellis encoded information by assigning a different number of bits to adjacent tones or adjacent tone pairs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application having Ser. No.09/766,255, filed on Jan. 17, 2001 now U.S. Pat. No. 7,088,781 entitled:“Tone Ordered Discrete Multitone Interleaver,” and which is acontinuation-in-part of U.S. utility application entitled, “DiscreteMultitone Interleaver,” having Ser. No. 09/736,353, filed Dec. 14, 2000(now U.S. Pat. No. 7,099,401 U.S. utility application Ser. No.09/736,353 claims priority to U.S. provisional application entitled,“Discrete Multi-Tone Trellis Interleaver,” having Ser. No. 60/170,891,filed Dec. 15,1999 U.S. utility application Ser. No. 09/736,353 and U.S.provisional application No. 60/170,891 are entirely incorporated hereinby reference.

TECHNICAL FIELD

The present invention generally relates to communications and modems,and more particularly to a tone ordered discrete multitone interleaversystem and method for efficiently minimizing noise distortion andenhancing data transmission communications.

BACKGROUND OF THE INVENTION

Communications devices, particularly those that implement digitalsubscriber line (DSL) technologies (e.g., T1 and xDSL, including SDSL,HDSL, ADSL, etc.), transmit high speed data using analog signals overtelephone connections, which are typically copper wire pairs. Theconnections and equipment are subject to adverse impulse noise. Impulsenoise events are likely correlated over several symbol (or baud) periodsof the DSL modulation. Correlated noise or distortion undesirably willsignificantly degrade performance of the decoder associated with areceiver.

In order to minimize the adverse affects of noise, various forward errorcorrection coding techniques (also known as convolutional coding) havebeen developed and employed in the past. Typically, in forward errorcorrection coding, at the transmitter, data bits are encoded by addingredundant bits systematically to the data bits so that, normally, onlypredetermined transitions from one sequential group of bits(corresponding to a symbol, or baud) to another are allowed. There is aninherent correlation between these redundant bits over consecutivebauds. At the receiver, each baud is tentatively decoded and thenanalyzed based on past history, and the decoded bits are corrected, ifnecessary.

One well known and widely accepted error coding technique is trelliscoded modulation (TCM), which is a form of convolutional coding that isoptimized according to a specific modulation scheme. A TCM encoder issituated at the transmitter, and a TCM decoder is situated at thereceiver. TCM is highly desirable since it combines the operations ofmodulation and error coding to provide effective error control codingwithout sacrificing power and bandwidth efficiency. The TCM decoderessentially averages the noise over more than one of the symbols.However, noise that is correlated over the constraint length of thetrellis code will effectively degrade performance. In many cases,correlated noise causes the trellis decoder to perform worse than if thereceiver employed no trellis coding at all.

As examples, U.S. Pat. No. 5,659,578 to Alamouti et al. and U.S. Pat.No. 4,677,625 to Betts et al. describe the concept of TCM. The latterdescribes a distributed trellis encoder that can be used to spreadsymbols associated with a data stream over time across successive symbol(baud) periods. This distributed encoder significantly improvesperformance by making the transmissions less susceptible to errorsresulting from imposition of correlated noise. U.S. Pat. Nos. 5,659,578and 4,677,625 are entirely incorporated herein by reference.

The various DSL technologies employ a variety of line coding, e.g. 2Binary, 1 Quaternary (2B1Q), Quadrature Amplitude and Phase modulation(QAM), Carrierless Amplitude and Phase (CAP) modulation, and DiscreteMultitone (DMT). DMT is now the standard line coding for AsymmetricalDigital Subscriber Line (ADSL) as specified in international standardspublished by the ITU (International Telecommunication Union) asRecommendations G.992.1 Series G: Transmission Systems and Media,Digital Systems and Networks, Digital Transmission Systems—AccessNetworks ADSL Transceivers, and G.992.2 Splitterless ADSL transceivers.G.992.1 and G.992.2 are available from the ITU, Geneva, Switzerland, athttp://www.itu.int and are entirely incorporated herein by reference.

DMT is a Frequency Division Multiplex (FDM) type of modulation in whichan incoming bit stream is multiplexed into a number of sub-carriers orsub-channels. DMT as used in ADSL enables a digital subscribertechnology capable of delivering high-speed digital information overexisting unshielded twisted pair copper telephone lines

DMT encodes data on multiple sub-carriers, referred to as tones, thatare then converted to time domain signals for transmission by an InverseDiscrete Fourier Transform (IDFT). An additional level of line coding,e.g. QAM, can be employed within each of the tones. A DMT trellisencoder generally codes between adjacent tones. DMT uses a DiscreteFourier Transform (DFT) to demodulate the tones.

The DMT 16-state trellis code constraint length is approximately four4-dimensional symbols. Four-dimensional symbols are encoded as two2-dimensional constellations on two tones. Four 4-dimensional symbolsare thus encoded over eight tones. DMT suffers from performancelimitations including sinx/x coupling of energy between adjacent tones.DMT convolutional encoders operate “serially” on mapped constellationssuch that consecutively generated constellations are mapped to adjacenttones. (Sin x)/x coupling allows noise on one tone to affect adjacenttones. Correlated noise on adjacent tones, particularly that within theDMT code constraint length, contributes to multiple metric calculationsin the trellis decoder. Correlated noise in consecutive metriccalculations causes negative gain and can result in a worse performancethan if no coding was employed.

DSL technologies are still in a state of infancy and are being improvedover time by engineers and designers. The industry still needs ways tofurther enhance DSL communications and, in particular, ways to minimizethe adverse effects of impulse noise and correlated noise. Thus, aheretofore unaddressed need exists in the industry to address theaforementioned deficiencies and inadequacies.

SUMMARY OF THE INVENTION

The present invention provides a system for a tone ordered discretemultitone interleaver and a method for tone ordered interleaving acrossDMT tones. Several embodiments of tone ordered discrete multitoneinterleaving are described below.

The tone ordered discrete multitone trellis interleaver spreads trellissymbols across several carrier tones such that the metrics in thereceiver are not correlated. The depth of the interleaver will determinethe number of tones used to spread the symbol.

Noise impacting adjacent tones will not appear in the metriccalculations until a number of trellis symbols later, the number beingequal to the depth of the interleaver. In effect, the tone ordereddiscrete multitone trellis interleaver causes the symbols to skip overcorrelated noise.

Related application Ser. No. 09/736,353 entitled “Discrete MultitoneInterleaver” describes several discrete multitone interleavers andmethods for tone ordered interleaving across DMT tones. Some of thedescribed systems and methods show synchronized switches that may bedifficult or expensive to implement in integrated circuits. Though notlimited to integrated circuits, the tone ordered discrete multitoneinterleaver addresses the potential difficulties and expenses associatedwith implementing discrete multitone interleaving in integratedcircuits.

Briefly described, in architecture, the system can be implemented in atransmitter and a receiver as follows. In the transmitter the toneordered discrete multitoned interleaver includes a tone ordering elementcapable of assigning bits to a plurality of tones, and a bit and gaintable, capable of designating that within a portion of the plurality oftones, a variable plurality of bits is assigned to each of the pluralityof tones, and wherein the variable plurality of bits assigned to each ofthe plurality of tones is different from the variable plurality of bitsassigned to each adjacent tone. Several non-exclusive ways to determinethe variable plurality of bits to be assigned to the tomes are provided.The tone ordered discrete multitone deinterleaver receiver includes abit ordering element that performs a complementary re-ordering of thedata coded by the transmitter.

The present invention can also be viewed as providing a method fortransmitting tone ordered discrete multitoned interleaved data. In thisregard, the method of transmitting data can be broadly summarized by thesteps of: receiving bits and relative gain information designating avariable plurality of bits to be assigned to each of a plurality oftones, wherein the variable plurality of bits to be assigned to each ofthe plurality of tones is different from the variable plurality of bitsto be assigned to each adjacent tone; and assigning bits to theplurality of tones based on the bits and relative gain information. Themethod of receiving data involves the step of reordering the dataencoded by the tone ordered discrete multitoned interleaver.

In addition to other advantages described above, the tone ordereddiscrete multitone trellis interleaver provides improved coding gain.The tone ordered discrete multitone trellis interleaver provides theseadvantages without an increase in delay since the interleaving occursbetween tones rather than between symbols in time.

Other systems, methods, features, and advantages of the presentinvention will be or become apparent to one with skill in the art uponexamination of the following drawings and detailed description. It isintended that all such additional systems, methods, features, andadvantages be included within this description, be within the scope ofthe present invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawings. The components in the drawings are not necessarily to scale,emphasis instead being placed upon clearly illustrating the principlesof the present invention. Moreover, in the drawings, like referencenumerals designate corresponding parts throughout the several views.

FIG. 1 is a block diagram of an ADSL transceiver system including anADSL remote transceiver and an ADSL central transceiver.

FIG. 2 is a block diagram of an ADSL DMT transmitter that resides in theADSL remote transceiver and the ADSL central transceiver of FIG. 1. TheADSL DMT transmitter includes a tone ordering element.

FIG. 3 is a graph showing an exemplar non-interleaving assignment ofbits to tones as might be made by the tone ordering element. Thenon-interleaving assignment of bits to tones shows an assignment asmight be made when the tone ordered discrete multitone interleaver isoptionally disabled or as might be made in the prior art.

FIG. 4 is a graph showing an exemplar interleaving assignment of bits totones using the tone ordered discrete multitone interleaver.

FIG. 5 is a block diagram of an ADSL DMT receiver that resides in theADSL remote transceiver and the ADSL central transceiver of FIG. 1. TheADSL DMT receiver includes a bit ordering element.

DETAILED DESCRIPTION

The tone ordered discrete multitone interleaver system and associatedmethods will be specifically described hereafter in the context of atransmitter and a receiver at each end of DSL communication channel. Thetone ordered discrete multitone system and associated methods asdescribed in this context are intended to be possible nonexclusiveexamples of implementations. Numerous other embodiments are envisionedand are possible, as will be apparent to those with skill in the art.

The tone ordered discrete multitone interleaver system of the presentinvention allows trellis coding over multiple DMT tones. Although notlimited to this particular application and any particular number oftones, the tone ordered discrete multitone interleaver system isparticularly suited for use in connection with modems at opposing endsof telephone connections (wire pairs) extending between a central office(CO; defined as any facility having a telephone switch) associated witha telephone company and a customer premises (CP). The modems can employany suitable modulation scheme, for example but not limited to, thatprescribed by the industry standard V.34 that has been promulgated bythe International Telecommunications Union (ITU). Many CPs already havetwo-wire pairs connecting them to the CO. The tone ordered discretemultitone interleaver system can effectively average the noise overmultiple tones, for example, eight different tones, yielding betterperformance and longer DSL reach between the CO and CP equipment. Insome cases, the tone ordered discrete multitone interleaver systemprovides data throughput where none was possible otherwise.

Note that in the embodiments, as described hereafter, the transmittersand receivers can be implemented in hardware, software, firmware, or acombination thereof. Preferably, all of the component parts of each,except the amplifier and transformer elements, are implemented infirmware that is stored in a memory (EPROM) and that is executed by asuitable instruction execution system, particularly, a digital signalprocessor (DSP) or general purpose microprocessor. The software/firmwarecan be stored and transported on any computer readable medium. Ifimplemented in hardware, in whole or in part, as in alternativeembodiments, the hardware components can be implemented with any or acombination of the following technologies, which are all well known inthe art: a discrete logic circuit(s) having logic gates for implementinglogic functions upon data signals, an application specific integratedcircuit (ASIC) having appropriate combinational logic gates, aprogrammable gate array(s) (PGA), a field programmable gate array(FPGA), etc. The tone ordered discrete multitone interleaver may beparticularly useful when discrete multitone interleaving, as describedherein and in related application Ser. No. 09/736,353, is implemented inan ASIC.

Any process descriptions or blocks in figures should be understood asrepresenting modules, segments, or portions of code which include one ormore executable instructions for implementing specific logical functionsor steps in the process, and alternate implementations are includedwithin the scope of the embodiments of the present invention in whichfunctions may be executed out of order from that shown or discussed,including substantially concurrently or in reverse order, depending onthe functionality involved, as would be understood by those reasonablyskilled in the art of the present invention.

The tone ordered discrete multitone interleaver program, which comprisesan ordered listing of executable instructions for implementing logicalfunctions, can be embodied in any computer-readable medium for use by orin connection with an instruction execution system, apparatus, ordevice, such as a computer-based system, processor-containing system, orother system that can fetch the instructions from the instructionexecution system, apparatus, or device and execute the instructions. Inthe context of this document, a “computer-readable medium” can be anymeans that can contain, store, communicate, propagate, or transport theprogram for use by or in connection with the instruction executionsystem, apparatus, or device. The computer readable medium can be, forexample but not limited to, an electronic, magnetic, optical,electromagnetic, infrared, or semiconductor system, apparatus, device,or propagation medium. More specific examples (a non-exhaustive list) ofthe computer-readable medium would include the following: an electricalconnection (electronic) having one or more wires, a portable computerdiskette (magnetic), a random access memory (RAM) (electronic), aread-only memory (ROM) (electronic), an erasable programmable read-onlymemory (EPROM or Flash memory) (electronic), an optical fiber (optical),and a portable compact disc read-only memory (CDROM) (optical). Notethat the computer-readable medium could even be paper or anothersuitable medium upon which the program is printed, as the program can beelectronically captured, via for instance optical scanning of the paperor other medium, then compiled, interpreted or otherwise processed in asuitable manner if necessary, and then stored in a computer memory.

FIGS. 1-4 show one embodiment of the tone ordered discrete multitoneinterleaver. FIG. 5 shows one embodiment of the tone ordered discretemultitone deinterleaver for deinterleaving data processed by the toneordered discrete multitone interleaver.

FIG. 1 shows a block diagram of an ADSL DMT transceiver system 100showing the basic functional blocks and interfaces. The ADSL transceiversystem includes an ADSL remote transceiver (ADSL Transceiver-R) 102, achannel 104, and an ADSL central transceiver (ADSL Transceiver-C) 106.The ADSL Transceiver-R 102 is typically housed in an ADSL DMT modem 112.The ADSL Transceiver-C 106 is typically housed in a Digital SubscriberLine Access Multiplexer (DSLAM) 124. ADSL DMT transceiver system 100shows a transmission system and method for data transport. Remote powerfeeding, which may be provided by the ADSL Transceiver-C 106 is notshown.

In the ADSL DMT transceiver system 100, an ADSL circuit connects ADSLTransceiver-R 102 and ADSL Transceiver-C 106 on each end of atwisted-pair telephone line, creating three information channels—a highspeed downstream channel, a medium speed duplex channel, and a plain oldtelephone service (POTS) channel. The POTS channel is split off from thedigital modems by filters, thus guaranteeing uninterrupted POTS. Thehigh speed channel ranges from 1.5 to 8 Mbps, while duplex rates rangefrom 16 Kbps to 1 Mbps. Each channel can be submultiplexed to formmultiple, lower rate channels.

The ADSL Transceiver-R 102 is typically located at a customer's premiseand the ADSL Transceiver-C 106 is typically located at a telephonecompany's central office or remote location. As is known in the art, theADSL Transceiver-C 106 acts as a master to some functions of the ADSLTransceiver-R 102. In a typical application, transmitter and receivercomponents will be incorporated into the same device so that each iscapable of transmitting and receiving data. The tone ordered discretemultitone interleaver and associated tone ordered discrete multitonedeinterleaver are incorporated into an ADSL DMT transmitter and an ADSLDMT receiver, respectively, at each end of the channel 104.

The ADSL Transceiver-R 102 includes an ADSL DMT transmitter 200,described in detail below and shown in FIG. 2. For ease in describingthe ADSL transceiver system 100, the detailed description is providedfrom the perspective of passing information from the transmitter in theADSL Transceiver-R 102 to the receiver in the ADSL Transceiver-C 106.Those skilled in the art will recognize an analogous analysis applies tothe transmission of information from the ADSL Transceiver-C 106 to theADSL Transceiver-R 102.

The ADSL DMT modem 112 may also contain a splitter 114 and othercomponents known to those skilled in the art. The input to the ADSLTransceiver-R 102 may be a remote network (Network-R) 110. The remotenetwork 110 may include service modules (SMs) 108. The service modules108 may be personal computers, servers, routers, and many other devicesknown to those skilled in the art. A standard phone 116, a voice bandfacsimile (V.B. Fax) 118, and an ISDN device may be connected to thesplitter 114. The splitter 114 contains filters that separate highfrequency ADSL signals from voiceband signals such as the standard phone116, the facsimile 118, and the ISDN device.

Prior to entering the channel 104, the signal from the ADSL DMT modem112 passes through a loop interface remote terminal end (U-R) 120. TheU-R 120 may be Synchronous Transfer Mode (STM) bit sync based orAsynchronous Transfer Mode (ATM) cell based.

The output of the loop interface remote terminal end 120 is passedthrough the channel 104 to the loop interface central office end (U-C)122. As with the loop interface remote terminal end 120, loop interfacecentral office end 122 may be Synchronous Transfer Mode (STM) bit syncbased or Asynchronous Transfer Mode (ATM) cell based.

The ADSL DMT transmitter 200, within the ADSL Transceiver-R 102,processes the service modules 108 and remote network 110 signals fortransmission to the ADSL DMT receiver 502, within the ADSL Transceiver-C106, via the channel 104. The ADSL DMT transmitter 200 processingincludes the tone ordered discrete multitone interleaving of the currentinvention. The ADSL DMT receiver 502 de-processes the signal and passesthe deprocessed signals to the Broadband (B-Band) Network 128 and thenarrowband (N-Band) network 130. The ADSL Transceiver-C 106 is housed inthe DSLAM 124 along with a DSLAM splitter 126 and other components knownto those skilled in the art. The ADSL DMT receiver 502 is housed in theADSL Transceiver-C 106, de-processing includes the tone ordered discretemultitone deinterleaving of the invention.

FIG. 2 is a block diagram of an ADSL DMT transmitter 200 that resides inthe ADSL Transceiver-R 102 and the ADSL Transceiver-C 106 of FIG. 1. Thebasic functional blocks of the ADSL DMT transmitter 200 are shown inFIG. 2. It should be noted that the components shown in FIG. 2 are notall required to construct a DMT transmitter. Instead, the components aremodels for facilitating the construction of DMT signal waveforms. Thosewaveforms may be constructed in a variety of ways including by hardware,software, and firmware.

The ADSL DMT transmitter 200 receives input(s) from service modules 108or remote network(s) 110. The multiplexor synchronous control element(Mux/Sync Control) 202 accepts the inputs and converts the inputs intomultiplexed and synchronized data frames (mux data frames). Themultiplexor synchronous control element 202 generates the mux dataframes at a nominal 4 k baud.

The mux data frame output of the multiplexor synchronous control element202 passes to the tone ordering element 208 by one of two paths, eachcarrying a binary data stream. The first binary data stream is a “fast”path that provides low latency. The second binary data stream isinterleaved and provides a low error rate and results in a higherlatency. Both paths are processed by a scrambler and forward errorcorrector (FEC) 204. The tone ordering element 208 receives binary datastream input from two paths in this embodiment. However, it is notcritical to the tone ordering element 208 how it receives input, or theform of the input, as long as the input is in the form of a bit stream,or can be converted into a bit stream.

The FEC is generally a Reed-Solomon coder. The scramblers, within theScrambler & FECs 204, are applied to the binary data streams withoutreference to any framing or symbol synchronizations. Descrambling in theADSL DMT receiver 502 can likewise be performed independent of symbolsynchronization. The interleaved path is processed by an interleaver 206in addition to a scrambler and FEC 204. The interleaver 206convolutionally interleaves the Reed-Solomon codewords. The depth of theinterleaving is a variable power of 2. The FEC can reliably correctoccasional errors if the data is interleaved. However, the FEC is noteffective in correcting all (sin x)/x distortion.

Both binary data stream paths are also processed by cyclical redundancychecks (CRCs) that are not shown in FIG. 2. The output of both paths isin the form of FEC data frames generated at the DMT symbol rate. An FECdata block may span more than one DMT symbol.

The fast and interleaved paths lead to the tone ordering element 208.The tone ordering element 208 combines data frames from the fast and theinterleaved paths into combined tone ordered data symbols on tones. Thetone ordering element 208 first places bits from the fast andinterleaved paths into an original bit table b_(i) and then orders thebits in an ordered bit table b′_(i). Those skilled in the art willrecognize that the original bit table b_(i) and the ordered bit tableb′_(i) table may be any system, computer program, hardware device,memory element, or logic device, that organizes information in a readilyretrievable manner.

The number of bits per tone and the relative gains to be used for everytone are calculated by the ADSL DMT receiver 502 and sent to the ADSLDMT transmitter 200 according to a protocol defined by ITU standards.The pairs of numbers, representing the bits per tone and the relativegains, are typically stored in ascending order of frequency or tonenumber i, in a bit and gain table. As with the original bit table b_(i)and the ordered bit table b′_(i) table, the bit and gain table may beany system, computer program, hardware device, memory element, or logicdevice, that organizes information in a readily retrievable manner. Thebit and gain table may be two separate systems that are coordinated byany other device so that bit and gain information is available for theassignment of bits to tones. The bit and gain table is one means ofproviding bits and relative gain information. In this application, inthe phrase “bits and relative gain information” the word “information”refers to “bits” and “relative gains” (information regarding theassignment of bits and the relative gains to be used for every tone)—incontrast to an interpretation of the phrase as “logical bits plusrelative gain information.”

The tone ordering element 208 first assigns bits from the fast path tothe tones with the smallest number of bits assigned to them and thenassigns the bits from the interleaved path to the remaining tones. Alltones are encoded with the number of bits assigned to them. Therefore,some tones may have a mixture of bits from the fast and interleavedpaths.

As described in ITU G.992.1, the ordered bit table b′_(i) is based onthe original bit table b_(i) as follows for k=0 to 15:

First, From the bit and gain table, find the set of all i with thenumber of bits per tone b_(i)=k; and

Second, assign b_(i) to the ordered bit table b′_(i) in ascending orderof i.

FIG. 3 is a graph showing an exemplar non-interleaving assignment ofbits to tones as might be made by the tone ordering element 208 in theprior art or when the dynamically selectable tone ordering discretemultitone interleaver is not operational. As shown in FIG. 3, adjacenttones often carry the same number of information bits. Since all tonescarrying the same number of information bits b_(i) are trellis encodedconsecutively by the constellation encoder and gain scaler 210, adjacenttones are generally not interleaved in the prior art.

FIG. 4 is a graph showing an exemplar interleaving assignment of bits totones using the tone ordered discrete multitone interleaver. In contrastto the prior art, the tone ordered discrete multitone interleavermodifies the number of bits assigned to adjacent tone pairs so thatadjacent tones have a different number of bits assigned to them. Thismay be accomplished by forcing the receiver to instruct the transmitterto modify the original bit density (the theoretical bit density thatwould have resulted without the use of the tone ordered discretemultitone interleaver) on alternate tones or tone pairs. Thismodification forces interleaving of adjacent tones when tones carryingthe same number of information bits b_(i) are trellis encodedconsecutively. Those skilled in the art will recognize that it may notbe necessary to calculate the original bit density for the tone ordereddiscrete multitone interleaver to assign bits to tones. Those skilled inthe art will also recognize that it is not necessary to rely on thereceiver to instruct the transmitter to modify the original bit density.

In ADSL, the trellis encoder in the constellation encoder and gainscaler 210 is a 4-dimensional trellis encoder in which one trellissymbol is encoded as two 2-dimensional (complex arithmetic) signals ontwo tones. Therefore, tone pairs may be encoded together theninterleaved, or adjacent tones may be avoided. Turbo codes will also beimproved with the tone ordered discrete multitone interleaver.

Several interleaving tone ordering modifications are available. Amongthe available modifications, three are noted. First, the constellationdensity may be reduced by one bit on every alternate tone that has anoriginal bit density of b_(i). This option will never cause a loss inmargin but could reduce the data rate by 25%.

Second, the power gain scalars can be modified to compensate for theconstellation density. An increase in power on some tones increases thedensity of those tones while a decrease in power on other tonesdecreases their density. This option results in a higher overall datarate.

Third, the tone ordered discrete multitone interleaver may bedynamically discriminatory. The receiver may identify specific sets oftones that are degraded by correlated noise and apply the tone ordereddiscrete multitone interleaver only to those tones. If the dynamicallydiscriminatory tone ordered discrete multitone interleaver is enabled,then the trellis encoder, within the constellation encoder and gainscaler 210, will process the bits on selected tones in a newnon-sequential order.

The tone ordered discrete multitone interleaver can be used in place of,or in addition to, the original tone ordering function which constructsthe re-ordered bit allocation table b′_(i). Regardless of whichmodification to the ordering of bits on tones is used, the modificationmay be dynamically selectable by the receiver when the receiver senses adegradation of the incoming signal due to correlated noise.

Those skilled in the art will recognize that where the tone ordereddiscrete multitone interleaver boosts power in one or more tones, areduction in power in other tones will be required in order to returnthe system to equilibrium.

Though several embodiments of the tone ordered discrete multitoneinterleaver have been described, any system for selecting points out oforder by switching the input to the convolutional encoder willeffectively interleave the DMT data symbols. Selecting points out oforder may be done on consecutive points or may be done randomly.

Returning to FIG. 2, the tone ordered data symbols are passed to theconstellation encoder and gain scaler 210. The constellation encoder andgain scaler 210 converts the tone ordered data frames into coded bits onDMT tones. The constellation encoder and gain scaler 210 includes aconvolutional encoder coset mapper as described in ITU (InternationalTelecommunication Union) Recommendations G.992.1, Section 7.8. Theconstellational encoder, within the constellation encoder and gainscaler 210, is similar to a Quadrature Amplitude Modulation (QAM)encoder. The performance of the constellation encoder and gain scaler210 is improved by block processing Wei's 16-state, 4-dimensionaltrellis code.

The coded bits on DMT tones from the constellation encoder and gainscaler 210 are passed on to the Inverse Discrete Fourier Transformer(IDFT) 212. The IDFT 212 combines the QAM constellations and convertsthe bits on the DMT tones to output samples. The output samples areconverted to a serial stream by the parallel/serial buffer 214.

The serial stream from the parallel/serial buffer 214 is passed to adigital to analog converter (DAC) 216. The DAC 216 and associated analogprocessing blocks (not shown) construct a continuous transmit voltagewaveform corresponding to the discrete digital input samples from theIDFT 212.

The analog signal passes through the splitter 114 and the loop interfaceremote terminal end 120 and enters the channel 104.

FIG. 5 is a block diagram of an ADSL DMT receiver 502 that resides inthe ADSL remote transceiver 102 and the ADSL central transceiver 106 ofFIG. 1. FIG. 5 includes a tone ordered discrete multitone deinterleaverfor decoding and deinterleaving DMT symbols coded and interleaved by thetone ordered discrete multitone interleaver of FIGS. 1 and 2. The ADSLDMT receiver 502 receives an input signal at a splitter 126 from thechannel 104 and through the loop interface central office end 122. Thesignal includes narrowband signals that are split by the splitter 126and sent to the narrow band network 130.

The broadband portion of the signal from the channel 104 is processed byan analog to digital (ADC) converter 504 and a serial/parallel converter506 and demodulated by a Discrete Fourier Transformer (DFT) element 508.

DFT element 508 includes complementary gain scaling to that in thetransmitter constellation encoder and gain scaler 210. The DET element508 passes the demodulated signal to convolutional decoder 510. Theconvolutional decoder 510 includes a Viterbi decoder. The convolutionaldecoder 510 passes the output to a bit ordering element 514. The bitordering element 514 performs a complementary re-ordering procedure fromthat performed by the tone ordering element 208 including performing acomplementary re-ordering procedure from that performed by the toneordered discrete multitone interleaver. Those skilled in the art areable to determine the reordering procedure based on the performance ofthe tone ordering element 208.

The fast and the interleaved portions of the signal are segregated andsent down separate paths to the multiplexor synchronous control element520. The interleaved path is processed by a deinterleaver 516 and an FECand De-Scrambler 518. The fast path is only processed by an FEC andDe-Scrambler 518. The multiplexor synchronous control element 520 passesthe deinterleaved and convolutionally decoded signal to the broadbandnetwork 128.

Those skilled in the art will recognize there may be additionalcomponents involved in processing signals beyond those shown in theFIGS. 1, 2 and 5. In particular, there may be components involved inprocessing the signal between the DFT 508 and convolutional decoder 510(with associated mapper); and between the convolutional decoder 510 andthe bit ordering element 514. These additional components do not alterthe basic invention as described in FIGS. 1-5.

It should be emphasized that the above-described embodiments of thepresent invention, particularly, any “preferred” embodiments, are merelypossible examples of implementations, merely set forth for a clearunderstanding of the principles of the invention. Many variations andmodifications may be made to the above-described embodiment(s) of thetone ordered discrete multitone interleaver without departingsubstantially from the spirit and principles of the invention. All suchmodifications and variations are intended to be included herein withinthe scope of this disclosure and the present invention and protected bythe following claims.

1. A transmitter comprising: a tone orderer configured to receive a dataframe having a plurality of data bits and to assign the plurality ofdata bits to a plurality of tones in accordance with an ordered bittable; and an interleaved convolutional encoder configured to receive afirst portion of the plurality of data bits and a second portion of theplurality of data bits, and further configured to combine the firstportion and the second portion of data bits in an interleaved manner toproduce a stream of trellis symbols with consecutive trellis symbols inthe stream assigned to nonconsecutive tones.
 2. The transmitter of claim1, wherein the nonconsecutive tones are separated by M positions in theordered bit table, where M is greater than
 1. 3. The transmitter ofclaim 2, wherein M is received from a remote transceiver that receivedthe stream of trellis symbols.
 4. The transmitter of claim 1, whereinthe nonconsecutive tones are a set of degraded tones, the set ofdegraded tones identified from the plurality of tones by a remotetransceiver that received the stream of trellis symbols.
 5. Thetransmitter of claim 4, wherein the set of degraded tones is a portionof the plurality of tones.
 6. The transmitter of claim 4, wherein theset of degraded tones is dynamically selectable by the remotetransceiver.
 7. The transmitter of claim 1, wherein a number of bits anda relative gain associated with at least one of the plurality of tonesis received from a remote transceiver that received the stream oftrellis symbols.
 8. A transmitter comprising: a bit extractor configuredto extract from a data buffer a first plurality of bits in a firstperiod, and to extract from the data buffer a second plurality of bitsin a second period, the second period separated from the first period byM periods where M is greater than 1; and an interleaved convolutionalencoder configured to interleave at least one data bit in the firstplurality and at least one data bit in the second plurality and tologically combine the interleaved bits to produce an interleavedconvolutionally encoded symbol.
 9. The transmitter of claim 8, wherein Mis received from a remote transceiver that received the convolutionallyencoded symbol.
 10. The transmitter of claim 8, wherein M is based onthe quality of a transmission path between the transmitter and remotetransceiver that received the convolutionally encoded symbol.
 11. Thetransmitter of claim 8, wherein the interleaved convolutional encoderfurther comprises: a variable unit time delay element configured tostore the at least one data bit in the first plurality and to output theat least one data bit in the first plurality after a time delay havingvalue M periods.
 12. The transmitter of claim 11, wherein M isdynamically configurable.
 13. The transmitter of claim 8, furthercomprising: a mapper configured to map a combination of the interleavedconvolutionally encoded symbol and non-interleaved data bits into atleast one constellation point.
 14. The transmitter of claim 8, furthercomprising: a tone orderer configured to assign each of a plurality ofdata bits in a frame to one of a plurality of tones in accordance withan ordered bit table.
 15. A transmitter comprising: means for extractinga first plurality of bits from a data buffer, the first plurality ofbits associated with at least one first tone specified in an ordered bittable, and for extracting a second plurality of bits from the databuffer, the second plurality of bits associated with at least one secondtone specified in the ordered bit table, the at least one second toneseparated in the ordered bit table by M tones from the at least onefirst tone, where M is greater than 1; and means for convolutionallyencoding at least a portion of the bits in the first plurality toproduce a first trellis symbol, and for convolutionally encoding atleast a portion of the bits in the second plurality to produce a secondtrellis symbol, and for outputting the second trellis symbol immediatelyfollowing the first trellis symbol.
 16. The transmitter of claim 15,wherein M is received from a remote transceiver that received the firstand second trellis symbols.
 17. The transmitter of claim 15, wherein Mis based on the quality of a transmission path between the transmitterand remote transceiver that received the first and second trellissymbols.
 18. The transmitter of claim 15, further comprising: means forassigning each of a plurality of data bits in a frame to one of aplurality of tones in accordance with the ordered bit table.
 19. Amethod comprising the steps of: receiving a data input bit X(m) at afirst symbol time, the input bit X(m) associated with a first tone;storing the data input bit X(m); receiving, after a delay of M symboltimes where M is greater than 1, a data input bit X(m+M) at a secondsymbol time m+M, the input bit X(m+M) associated with a second toneseparated by M tones in an ordered bit table; outputting the stored datainput bit X(m) at the second symbol time m+M; and logically combiningthe data input bit X(m+M) and the outputted data input bit X(m) toproduce a trellis symbol.
 20. The method of claim 19, further comprisingthe step of: receiving M from a remote modem.
 21. The method of claim19, wherein M is based on the quality of a transmission path between aremote modem and a local transmitter performing the method.
 22. Themethod of claim 19, further comprising the step of: extracting the datainput bit X(m) and the data input bit X(m+M) from a data buffer inaccordance with the ordered bit table.
 23. The method of claim 19,further comprising the step of: mapping a combination of the trellissymbol and uncombined data bits into at least one constellation point.24. The method of claim 19, further comprising the step of: assigningdata input bit X(m) and data input bit X(m+M) to one of a plurality oftones in accordance with the ordered bit table.